Various types of catheter instruments have been suggested or disclosed in the patent literature for effecting non-invasive or minimally invasive surgical or medical procedures within the body of a person or animal. For example, in U.S. Pat. No. 4,445,509 (Auth) there is disclosed a recanalization catheter designed specifically for cutting away hard, abnormal deposits, such as atherosclerotic plaque from the inside of an artery while supposedly preserving the soft arterial tissue. That recanalizing catheter includes a sharp-edged, multi-fluted, rotating cutting tip mounted at the distal end of the catheter and arranged to be rotated by a flexible drive shaft extending down the center of the catheter. The rotation of the cutting head is stated as producing a "differential cutting" effect, whereupon relatively hard deposits are cut away from relatively soft tissue. Suction ports are provided in the cutting tip to pull the hard particles produced by the cutting action into the catheter for removal at the proximal end thereof so that such particles thereof so that such particles do not flow distally of the catheter where they could have an adverse effect on the patients' body.
It has been determined that the use of sharp rotary cutting blades in a revascularization catheter can have various adverse effects on arterial tissue, e.g., snagging, cutting, or otherwise damaging the tissue of the artery wall.
In our U.S. Pat. No. 4,700,705 (Kensey et al.), assigned to the same assignee as this invention, and whose disclosure is incorporated by reference herein, there is disclosed and claimed catheters and methods of use for effecting the opening of a vessel, duct or lumen, such as the opening of a atherosclerotic restriction in an artery or the opening of a fallopian tube. The catheters of that invention consist of elongated flexible members of sufficient flexibility to enable them to be readily passed through the body of the patient to the situs of the procedure to be accomplished, e.g., the location of the atherosclerotic plaque in the artery to be opened. A working head is mounted at the distal end of the catheter and is arranged for high-speed rotation about the longitudinal axis of the catheter. In some embodiments the catheter may eject fluid at the working head to expedite the procedure.
In another of our U.S. patents, namely, U.S. Pat. No. 4,747,821 (Kensey et al.) (hereinafter referred to as the '821 patent), also assigned to the same assignee as this invention and whose disclosure is incorporated by reference herein, there is disclosed and claimed other catheters particularly suited for revascularization of arteries. Each of those catheters includes a rotary working head having at least one non-sharp impacting surface to effect material removal without cutting. Moreover, those catheters are arranged to eject fluid adjacent the working head to expedite the procedure. When such a catheter is used for treating atherosclerotic disease by recanalizing arteries, the catheter is guided through the vascular system of the patient to the site of the vascular occlusion or blockage (restriction) that has been determined to exist so that the rotary working head is located immediately adjacent the restriction. The working head is then rotated about the longitudinal axis of the catheter at a high rate of speed, e.g., from 10,000 rpm to 200,000 rpm. At the same time, fluid is passed through the catheter and out of its distal end adjacent the working head.
The opening of the restriction to allow freer flow of blood is effected by the dilation and/or selective emulsification properties of the catheter's working head. In this connection, during the rotation of the working head fluid jets exiting the distal end of the catheter at the working head or immediately accelerated laterally by portions of the working heads so that they are broken up into small segments that develop considerable momentum as they are flung out in all directions, including radial directions, toward the wall of the artery. These liquid segments transfer their momentum to the artery wall, forcing the artery wall outward laterally in all directions thereby aiding in dilating it. Moreover, the radial pressure developed by the rotating working head is substantial and can raise local static pressure immediately adjacent the working head by approximately 100 to 200 millimeter of Hg. This increased pressure on the artery wall contiguous with the rotating working head is not due solely to the impact of the liquid segments thereon, but also due to the recirculation of the liquid surrounding the working head. In this connection, the rotation of the working head produces a powerful, toroidal shaped vortex contiguous with the working head.
The vortex, in addition to augmenting the application of increased pressure to the artery wall contiguous with the working head, also has the effect of recirculating any particles that may have been broken off from the material forming the arterial restriction by the impact of the rotary working head with that material. In particular the working head, with its non-sharp impacting surfaces differentiates atherosclerotic tissue from normal tissue through the inherent differences in the tissues' physical properties and organizational patterns. Therefore, when the catheter is passed transluminally through the diseased artery, its working head serves to emulsify occlusive lesions not covered with fibrous plaque by repeatedly impacting the material forming the restriction as the working head is rotated, and with minimal risks of puncture or perforation of the contiguous artery wall. The emulsification process is accomplished by the repeated impaction of the non-sharp impacting surfaces on the material forming the restriction. This action causes the material to be broken away in small particles. The vortex flow at the working head insures that any particles produced by the impacting action are drawn back into contact with the impacting surfaces of the rotating working head. Accordingly, those particles are repeatedly impacted over and over, with each impaction reducing the size of the particles further until the resulting particle size is sufficiently small, e.g., 95% have a surface area less than that of a red-blood cell, that they can be permitted to flow to downstream tissue without causing any significant deleterious effects to the patient.
Other catheters for enlarging an opening in a vessel, duct or lumen have been disclosed and claimed in the following United States patents, assigned to the same assignee of this invention, and whose disclosures are also incorporated by reference herein: U.S. Pat. No. 4,589,412 (Kensey); U.S. Pat. No. 4,631,052 (Kensey), U.S. Pat. No. 4,686,982 (Kensey et al.), U.S. Pat. No. 4,749,376 (Kensey et al.) and U.S. Pat. No. 4,790,813 (Kensey).
For some procedures involving the enlarging of openings in vessels, ducts and lumens, it may prove beneficial or more effective to utilize catheters whose working heads include impacting surfaces of differing aggressiveness which may be selectively brought into engagement with the restriction to be opened. Moreover, such catheters can be utilized to effect other procedures within the body of a living being, e.g., the destruction of stones or other hard bodies. Examples, of other prior catheters and/or instruments for destroying stones within the body of a living being are the following which are assigned to the same assignee as this invention: U.S. Pat. No. 4,679,558 (Kensey et al.) and U.S. Pat. No. 4,811,735 (Kensey et al.).
In our aforementioned application there is disclosed and claimed methods of revascularizing partially or fully occluded arteries utilizing a rotating working head having at least two impacting surfaces, one of more aggressiveness than the other. The subject invention relates to such methods.